1. Field of the Invention
This invention relates to polymeric compositions useful as insulation for wire and cable products. More specifically, the compositions of the invention are crosslinkable ethylene-vinyl ester copolymers which exhibit improved abrasion resistance.
2. Description of the Prior Art
Polymeric compositions exhibiting a balance of physical properties, processability and flame retardance comprised of a crosslinkable polymer, such as ethylene-vinyl acetate copolymer, silane(s) and hydrated inorganic filler(s) are known and have found wide acceptance in the wire and cable industry. Such compositions are disclosed in U.S. Pat. Nos. 3,832,326 and 3,922,442 to North et al and U.S. Pat. Nos. 4,349,605 and 4,381,362 to Biggs et al. Besides the polymer, silane and hydrated filler, the formulations also typically contain a crosslinking agent and other additives such as pigments, stabilizers, lubricants, antioxidants, and the like.
The compositions of North et al and Biggs et al are particularly useful for the insulation of switchboard wire, appliance wire and automotive wire where a combination of superior electrical properties combined with resistance to the degradative effects of heat and flame are essential and where low smoke density and non-corrosive fumes are desirable. They find particular use as white and colored insulation compositions which can be extruded over metal, e.g., copper or aluminum, conductors to provide a single layer insulating and jacketing composition which meets the automotive primary wire SAE J1128 standard and UL 125.degree. C. appliance wire and Type SIS wire standards.
In certain automotive applications where an insulated wire is enclosed in a tubular metal conduit, such as for antilock braking systems, friction between the metal and insulated wire can abrade the insulation and eventually wear away the insulation and cause electrical problems. It would be highly advantageous if readily processable crosslinkable flame retardant formulations with increased abrasion resistance were available.